The winner-take-all primary was worth 50 Republican National Convention delegates, by far the most of any primary state so far.

But the bigger prize was precious political momentum in the race to pick an opponent for Democratic President Barack Obama this fall

That belonged to Romney when he captured the New Hampshire primary three weeks ago, then swung stunningly to Gingrich when he countered with a South Carolina upset 11 days later.

Now it was back with the former Massachusetts governor, after a 10-day comeback that marked a change to more aggressive tactics, coupled with an efficient use of an overwhelming financial advantage.

About half of Florida primary voters said the most important factor for them was backing a candidate who can defeat Obama in November, according to early exit poll results conducted for The Associated Press and the television networks.

As in early contests in Iowa, New Hampshire and South Carolina, that mattered more than experience, moral character or conservative credentials.

Not surprisingly, in a state with an unemployment rate hovering around 10 percent, about two-thirds of voters said the economy was their top issue. More than 8 in 10 said they were falling behind or just keeping up. And half said that home foreclosures have been a major problem in their communities.

Gingrich swept into Florida from South Carolina, only to run headlong into a different Romney from the one he had left in his wake in South Carolina.

Romney, the former Massachusetts governor, shed his reluctance to attack Gingrich, the former House speaker, unleashing hard-hitting ads on television, sharpening his performance in a pair of debates and deploying surrogates to the edges of Gingrich's own campaign appearances, all in hopes of unnerving him.

Restore our Future, an outside group supporting Romney, accounted for about $8.8 million in the ad wars, and the candidate and the "super PAC" combined outspent Gingrich and Winning The Future, the organization backing him, by about $15.5 million to $3.3 million, an advantage of nearly 5-1.

Gingrich responded by assailing Romney as a man incapable of telling the truth and vowed to remain in the race until the Republican National Convention next summer. He won the endorsement of campaign dropout Herman Cain and increasingly sought the support of evangelicals and tea party advocates, a former House speaker running as the anti-establishment insurgent of the party he once helped lead.

Bombarded by harsh television advertising, some Floridians said they had soured on both candidates.

"The dirty ads really turned me off on Mitt Romney," said Dorothy Anderson, of Pinellas Park, adding she was voting for Gingrich. She said of Romney, "In fact if he gets the nomination, I probably won't vote for him."